Investigation into the Energy Performance of a Pump-Turbine Under High-Load Conditions: Energy Loss and Output Power Decline

Balanced investigation of impeller geometric effects on energy conversion and hydraulic loss in a pump as turbine under pump and turbine modes

Pump as turbine (PAT) is a key technology for industrial residual pressure-energy recovery. However, achieving satisfactory hydraulic performance under both pump and turbine operating modes remains challenging, primarily because the internal flow structure and energy conversion mechanism are altered during reverse operation, and the influence of geometric parameters on dual-mode performance remains unclear. In this study, the entropy production theory and vorticity transport analysis were combined to investigate the effects of geometric parameters on dual-mode hydraulic performance and flow mechanisms, elucidating the intrinsic relationship between vorticity generation and energy dissipation. The results indicate that the influence of blade geometric parameters on dual-mode performance is markedly asymmetric, which can be attributed to the reversal of the flow direction leading to changes in the velocity triangles. The blade wrap angle exhibits a strong positive correlation with efficiency in pump mode, whereas a negative correlation is observed in turbine mode. In pump mode, turbulent entropy production dominates, whereas wall entropy production increases in turbine mode. Vorticity transport analysis reveals that the Coriolis force term and the relative vorticity stretching term are the dominant mechanisms of vorticity generation, and their spatial distribution is consistent with that of the regions of high entropy production, indicating a strong correlation between vortex dynamics and irreversible energy dissipation. Velocity triangle analysis further demonstrates that the attack angle is the key parameter determining impact losses and separation losses. The parameter coordination design strategy proposed in this study provides a theoretical basis and quantitative reference for achieving efficient dual-mode operation of PAT.

Research on Pressure Fluctuation and Vortex Evolution Characteristics in Pump-Turbine Under Load-Rejection Condition

During load rejection in pumped-storage power stations, the rotational speed of the pump-turbine increases abruptly. The consequent structural deterioration of the internal flow induces high-amplitude hydraulic excitations, posing a serious threat to the operational stability of the unit. This study investigates a Francis pump-turbine to elucidate its flow evolution and instability mechanisms during load rejection. The fluid is modeled as weakly compressible water to capture finite pressure wave propagation. Dynamic mesh simulates guide vane closure, while vortex identification and short-time Fourier transform analyze transient pressure pulsations. The results indicate that the transient process can be sequentially divided into four typical stages—turbine mode, turbine-braking mode, reverse-pump mode, and return-to-turbine mode—to account for the most critical periods during the load rejection transient. The unit exhibits the poorest stability near the maximum rotational speed (443.34 r/min), where flow reversal and the full development of vortex structures significantly amplify fluctuations in hydraulic thrust. The vaneless space is identified as the primary source of pressure pulsations, whose characteristics are dominated by rotor–stator interaction mechanisms, and such disturbances decay rapidly in the downstream direction. Under turbine-braking and reverse-pump conditions, vortex rings, backflow, and asymmetric vortex structures generated within the spiral casing collectively contribute to the severe deterioration of the internal flow field quality.

Transient Fluctuations in Hydraulic Performance and Energy Dissipation in a Tubular-Flow Pump with Highly Twisted Blades

Periodic fluctuations in pump head are a common unsteady phenomenon in tubular pumps; however, their underlying energy dissipation mechanism remains insufficiently understood. This study conducted transient numerical simulations on a two-blade tubular-flow pump with highly twisted blades operating at the design flow condition. Using entropy production theory, the research quantitatively examined Rotor–Stator Interaction (RSI), vortex development, and hydraulic loss characteristics. The findings reveal that turbulent entropy production is the primary contributor to total energy dissipation, while entropy generated by wall friction is minimal. Although the impeller experiences the greatest absolute energy loss, the fluctuations in entropy production within the guide vane are significantly larger. This indicates that the energy loss represented by the entropy production in the guide vane primarily drives the periodic head fluctuations of the pump. High entropy production is concentrated near both the leading and trailing edges of the guide vane, exhibiting a trough-shaped radial distribution influenced by the leading-edge hub vortex and tip leakage vortex. Additionally, the transient changes in entropy production under RSI are governed by the periodic formation and strengthening of the guide vane passage vortex, along with the shedding and breakdown of the wake vortex. Velocity analysis shows that the circumferential movement of the impeller wake continuously modifies the instantaneous inflow conditions at the guide vane’s leading edge, causing periodic changes in the incidence angle that enhance the passage vortex while weakening the wake vortex. This study provides deep insights into the operational stability of pumps and pumping stations in water transfer projects.

Quantitative Analysis of Windage Loss in Last Stage Blades of Steam Turbine

Performance Analysis of Side-by-Side Savonius Hydrokinetic Turbines Under Different Flow Velocities

The increasing demand for renewable energy has spurred the development of environmentally friendly technologies. Hydrokinetic turbines, which generate electricity from flowing water without dams or reservoirs, are a promising option. Among these, the Savonius turbine is ideal for low-flow conditions because of its simple design, ability to start on its own, and low maintenance needs. This study examines the performance of a side-by-side Savonius hydrokinetic turbine at inlet flow speeds of 0.2 m/s and 0.48 m/s using Computational Fluid Dynamics (CFD). The effect of TipSpeed Ratio (TSR) on performance was analyzed through the power coefficient (Cp) and moment coefficient (Cm) across a TSR range of 0.2-2.0. Transient simulations with the k-ω SST turbulence model captured unsteady flow around the rotating blades. Results show improved turbine performance with higher flow speeds. At 0.2 m/s, the maximum Cp was 0.180 at TSR = 1.0, and the highest Cm was 0.211 at TSR = 0.6. At 0.48 m/s, the maximum Cp reached 0.180 at TSR = 1.0, and the maximum Cm was 0.75 at TSR = 0.4. These results offer valuable insights for optimizing side-by-side Savonius turbines in low-flow water conditions.

Pump Turbines Under Near-Zero Flow Conditions: A Review of Flow Instabilities, Guide Vane Dynamics, and Mitigation Strategies

The grid volatility caused by the integration of wind and solar power poses challenges to power systems, where Pumped Storage Hydropower (PSH) plays an irreplaceable role. During start-up, shutdown, and mode transition of pump turbines, near-zero flow conditions frequently occur, leading to severe hydraulic instability, guide vane vibration, and abnormal noise. This review synthesizes field observations from multiple high-head pumped storage stations together with recent experimental, numerical, and theoretical studies. The review indicates that hydraulic instability is primarily associated with the coupled effects of clearance leakage flow, bi-stable flow, and Rotor–Stator Interaction (RSI). The review suggests that self-excited vibration, rather than forced resonance, dominates guide vane vibration and abnormal noise under near-zero flow conditions. Four mainstream regulation strategies are summarized, including Misaligned Guide Vanes (MGVs), start-up/shutdown sequence optimization, structural-parameter adjustment, and operating range avoidance. The applicability and limitations of each strategy are discussed. These findings provide support for the design and operation of high-head, large-capacity pump turbines.